The present application relates to a nanoparticle-resin composite material having transparency and a high refractive index in the visible light region and containing inorganic nanoparticles and a polymer or inorganic nanoparticles and a crosslinked product having a siloxane bond. Furthermore, the invention relates to a light-emitting device assembly using the nanoparticle-resin composite material and a filling material for the light-emitting device assembly.
Light-emitting device assemblies including light-emitting diodes (LED) or laser diodes (LD) have high luminance in spite of their small sizes, and are thus used in various applications, such as automobile stop lamps, signal lamps, field large displays, and the like. Such light-emitting device assemblies have recently been used as light sources for backlight of liquid crystal displays for cellular phones and large liquid crystal televisions because of the low power consumption and long lifetime.
In order to prevent direct contact of light-emitting devices and wiring with moisture and other corrosive gases and to further prevent physical damage to the light-emitting devices due to external force, light-emitting device assemblies generally have a structure in which, for example, as shown in FIG. 4, a sealing member 114 having an appropriate thickness is disposed on or above a light-emitting device 12. The sealing member 114 is generally composed of a transparent resin, such as an epoxy resin, a silicone resin, or an acrylic resin. However, usual light-emitting device assemblies have a large difference between the refractive indexes of the light-emitting device 12 and the sealing member 114 and thus has the problem that the efficiency of light emission is decreased by total reflection of part of light emitted from the light-emitting device 12 at the interface between the light-emitting device 12 and the sealing member 114 and re-absorption of the totally reflected light by the light-emitting device 12. In FIG. 4, reference numeral 11 denotes a reflection cup.
In order to solve this problem, Japanese Unexamined Patent Application Publication No. 2004-15063 discloses a technique in which nanoparticles having a particle diameter smaller than the wavelength of emitted light and a higher refractive index than that of a matrix resin are dispersed in the matrix resin to bring the effective refractive index of the resultant material near to that of a light-emitting device. In addition, Japanese Unexamined Patent Application Publication No. 2005-5740 discloses a resin material (sealing material) containing a resin and a filler such as titanium oxide or glass. Furthermore, PCT Japanese Translation Patent Publication No. 2004-537767 discloses an optical structure in which inorganic nanoparticles are blended with a polymer to control the refractive index.
As described above, a sealing member constituting a light-emitting device assembly is composed of an epoxy resin, a silicone resin, an acrylic resin, or the like, but an epoxy resin is frequently used. However, some problems to be resolved have been pointed out on resins for high-power light-emitting devices which have recently been in increasing demand. In Phys. Stat. Sol. (a) 194, No. 2, 380-388 (2002), it has been reported that epoxy resins have glass transition temperatures Tg of 100° C. to 150° C., and linear expansion coefficients increase above the glass transition temperatures Tg. When an epoxy resin is heated to the glass transition temperature Tg or more due to the heat generated in a light-emitting device, wiring connected to the light-emitting device may be disconnected. Therefore, the output of a light-emitting device is desirably limited to avoid the epoxy resin from being heated to the glass transition temperature Tg or more due to the heat generated in the light-emitting device. Furthermore, epoxy resins are discolored to yellow when being exposed to blue light, and thus the output from a light-emitting device assembly decreases with the passage of time. Therefore, silicone resins have recently been used as an alternative to epoxy resins.
However, Japanese Unexamined Patent Application Publication No. 2004-15063 discloses examples of combination of a matrix resin and nanoparticles in which the nanoparticles are dispersed in the matrix resin. In order to uniformly disperse the nanoparticles of several nanometers in the matrix resin without aggregation, for example, the nanoparticles may be chemically surface-treated for improving the affinity between the nanoparticles and the matrix resin. However, Japanese Unexamined Patent Application Publication No. 2004-15063 does not disclose such a technique. Also, Japanese Unexamined Patent Application Publication No. 2005-5740 does not disclose a technique for uniformly mixing a resin with a filler such as titanium oxide or glass without aggregation. PCT Japanese Translation Publication No. 2004-537767 shows an idea that a linker is used for activating the surfaces of inorganic nanoparticles, in order to disperse the inorganic nanoparticles in a polymer. However, this publication does not suggest a specific technique for properly dispersing the inorganic nanoparticles in the silicone polymer.
Silicone resins have excellent light resistance and are capable of suppressing a decrease in power in the use of blue light. Also, silicon resins have appropriate flexibility and are thus capable of suppressing an increase in stress even at high temperatures. However, silicon resins which are used in practical applications have reflective indexes of at most about 1.5 and are thus desired to have higher reflective indexes from the viewpoint of improvement in the efficiency of light emission.
Accordingly, it is desired to provide a nanoparticle-resin composite material (a composite material including inorganic nanoparticles and a polymer) having transparency and a reflective index of 1.55 or more in the visible light region, a light-emitting device assembly including the nanoparticle-resin composite material, and a filling material for the light-emitting device assembly.